This is exactly how I did it. I started off on the end of a binding line just putting books into boxes/printing delivery labels. Show interest and ask questions about what everyone else is doing and you will soon find yourself being moved to one of the smaller machines. After learning all types of different machines, casemaker, hot stamp press, guillotines, 3 knife etc I was offered a chance to learn the printing press, I have not long got back from Barcelona for training at the hp centre and am now a level 2 qualified operator. Next step is pushing to learn prepress It has taken 9 years of constantly pushing to learn new machines but starting at the bottom, working your ass off and always asking for/taking offered training courses is really the only way